3GPP (3rd Generation Partnership Project) LTE (long term evolution), which is an improvement of UMTS (Universal Mobile Telecommunications System), has been introduced as 3GPP release 8. 3GPP LTE uses OFDMA (orthogonal frequency division multiple access) in downlink, and SC-FDMA (Single Carrier-frequency division multiple access) in uplink. MIMO (multiple input multiple output) having maximum of 4 antennas has been adopted. Recently, discussions on 3GPP LTE-A (LTE-Advanced), the evolved 3GPP LTE, have been developing.
MDT (Minimization of Driving Tests) measurement is a method of test using terminals instead of vehicles which operators use for coverage optimization. The coverage varies depending on the location of the base station, arrangements of buildings around the test area and the environment of use of users. Therefore, the operator needs to perform driving tests periodically, requiring lots cost and resources. MDT enables the operator to measure the coverage by using a terminal.
MDT can be divided into logged MDT and immediate MDT. In logged MDT, the terminal performs MDT measurement and transfers the logged measurement to network at certain point of time. In immediate MDT, the terminal performs MDT measurement and transfers the measurement to network when reporting condition is fulfilled. Logged MDT performs MDT measurement in RRC idle mode while immediate MDT performs MDT measurement in RRC connection mode.
The operator can collect MDT measurements received from various terminals and produce a coverage map representing the distribution of availability of service and quality of services over the area the operator provides service for utilizing in network management and optimization. For example, when a problem of coverage in a certain area is reported from a terminal, the operator can extend the cell coverage of corresponding area by increasing transmit power of the base station providing service to the area.
In logged measurement, logging is carried out by the terminal and the logging of the results of measurement can be suspended or limited for various reasons. The terminal maintains the configuration for logging even when the logging is suspended. When the situation of suspension of the logging of the terminal is suspended is resolved, the terminal resumes logging according to the configuration maintained. When the logging is resumed after suspension, the results of the logging are not continuous in time. If the received logging results contain empty parts, the network can't identify the wireless environment and performance index for the empty parts. Therefore, there need a method for logging considering the situation where logging is suspended and/or resumed, and the device supporting the method.